Astronomy:2 Ceti

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Short description: Star in the constellation Cetus
2 Ceti
Location of 2 Ceti (circled in red)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Cetus
Right ascension  00h 03m 44.38784s[1]
Declination −17° 20′ 09.5719″[1]
Apparent magnitude (V) 4.483[2]
Characteristics
Evolutionary stage main sequence[3][4]
Spectral type B9 IVn[5]
U−B color index −0.12[6]
B−V color index −0.047±0.003[7]
Astrometry
Radial velocity (Rv)+8.0±4.6[8] km/s
Proper motion (μ) RA: +25.17[1] mas/yr
Dec.: −9.16[1] mas/yr
Parallax (π)11.98 ± 0.26[1] mas
Distance272 ± 6 ly
(83 ± 2 pc)
Absolute magnitude (MV)−0.06[7]
Details
Mass2.58[9] M☉
Radius3.92[9] R☉
Luminosity119+6
−5[4] L☉
Surface gravity (log g)3.66[9] cgs
Temperature11,419±388[10] K
Metallicity [Fe/H]+0.00±0.24[5] dex
Rotational velocity (v sin i)116[4] or 237[11] km/s
Age217[10] Myr
Other designations
Hydor, 2 Cet, BD−18°6417, FK5 905, HD 225132, HIP 301, HR 9098, SAO 147059[12]
Database references
SIMBADdata

2 Ceti, also named Hydor,[13] is a single[14] star in the equatorial constellation of Cetus, near the border with Aquarius. It is visible to the naked eye with an apparent visual magnitude of 4.483.[2] The distance to 2 Ceti can be estimated from its annual parallax shift of 12.0 mas,[1] which yields a value of around 272 light years. It appears to be moving further from the Earth with a heliocentric radial velocity of about +8 km/s.[8]

The stellar classification for this star is B9 IVn,[5] matching a B-type subgiant star with "nebulous" absorption lines due to rapid rotation.[15] Estimates of the rotation rate range from 116[4] to 237[11] km/s, and this high rate of spin is giving the star an equatorial bulge that is 12% larger than the polar radius.[15] 2 Ceti is about 217 million years old[10] with 2.6 times the mass of the Sun and 3.9 times the Sun's radius.[9] It is radiating 119 times the Sun's luminosity[4] from its photosphere at an effective temperature of 11,419 K.[10] An infrared excess has been detected around this star by the Akari satellite at a wavelength of 18μm, suggesting there is an orbiting debris disk.[16]

Naming

The ancient Greek term Hydor (ὕδωρ), meaning water, originally referred to a constellation of faint stars in the region of Aquarius and Cetus.[17] The IAU Working Group on Star Names approved the name Hydor for 2 Ceti, on 25 August 2025 and it is now so entered in the IAU Catalog of Star Names;[13] it had previously been used for λ Aquarii, for which the IAU adopted the Indian name Shatabhisha.[17]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V. 
  2. ↑ 2.0 2.1 Høg, E. et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics 355: L27–L30. Bibcode: 2000A&A...355L..27H. 
  3. ↑ Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 Zorec, J. et al. (2012). "Rotational velocities of A-type stars. IV. Evolution of rotational velocities". Astronomy and Astrophysics 537: A120. doi:10.1051/0004-6361/201117691. Bibcode: 2012A&A...537A.120Z. 
  5. ↑ 5.0 5.1 5.2 Wu, Yue et al. (2010). "Coudé-feed stellar spectral library – atmospheric parameters". Astronomy & Astrophysics 525: A71. doi:10.1051/0004-6361/201015014. Bibcode: 2011A&A...525A..71W. 
  6. ↑ Nicolet, B. (1964). "Catalogue of homogeneous data in the UBV photoelectric photometric system". Astronomy and Astrophysics Supplement Series 34: 1–49. Bibcode: 1978A&AS...34....1N. 
  7. ↑ 7.0 7.1 Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode: 2012AstL...38..331A. 
  8. ↑ 8.0 8.1 Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters 32 (11): 759–771. doi:10.1134/S1063773706110065. Bibcode: 2006AstL...32..759G. 
  9. ↑ 9.0 9.1 9.2 9.3 Stassun, Keivan G. et al. (2019). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal 158 (4): 138. doi:10.3847/1538-3881/ab3467. Bibcode: 2019AJ....158..138S. 
  10. ↑ 10.0 10.1 10.2 10.3 David, Trevor J.; Hillenbrand, Lynne A. (2015). "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal 804 (2): 146. doi:10.1088/0004-637X/804/2/146. Bibcode: 2015ApJ...804..146D. 
  11. ↑ 11.0 11.1 Royer, F. et al. (2007). "Rotational velocities of A-type stars". Astronomy and Astrophysics 463 (2): 671. doi:10.1051/0004-6361:20065224. Bibcode: 2007A&A...463..671R. 
  12. ↑ "2 Cet". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=2+Cet. 
  13. ↑ 13.0 13.1 "IAU Catalog of Star Names". https://exopla.net/star-names/modern-iau-star-names/. 
  14. ↑ Chini, R. et al. (2012). "A spectroscopic survey on the multiplicity of high-mass stars". Monthly Notices of the Royal Astronomical Society 424 (3): 1925–1929. doi:10.1111/j.1365-2966.2012.21317.x. Bibcode: 2012MNRAS.424.1925C. 
  15. ↑ 15.0 15.1 van Belle, Gerard T. (March 2012). "Interferometric observations of rapidly rotating stars". The Astronomy and Astrophysics Review 20 (1): 51. doi:10.1007/s00159-012-0051-2. Bibcode: 2012A&ARv..20...51V. 
  16. ↑ Ishihara, Daisuke et al. (May 2017). "Faint warm debris disks around nearby bright stars explored by AKARI and IRSF". Astronomy & Astrophysics 601: 18. doi:10.1051/0004-6361/201526215. A72. Bibcode: 2017A&A...601A..72I. 
  17. ↑ 17.0 17.1 "Hydor". IAU Working Group on Star Names. https://xing.fmi.uni-jena.de/mediawiki/index.php/Hydor. 



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